1. Technical Field
The present invention relates to a method for fabricating bump structures on semiconductor chips, in particular, to a method for fabricating under bump metallurgy structure (UBM structure) with panel type process.
2. Description of Related Art
Assembly mainly provides the functions such as integrated circuit protection, heat dissipation and circuit conducting, of which a wafer bumping process is usually applied to the flip chip. In advance of wafer stage, the UBM structure is formed on the external metal welding pad of the wafer, bumps are formed on the UBM structure, then the wafer is incised into multiple independent semiconductor chips. The semiconductor chip is connected to a package substrate through the bumps and then packaged with resin.
Refer to FIG. 1 to FIG. 6, wherein FIG. 1 is a schematic diagram of prior wafer bump fabrication process, and FIG. 2 to FIG. 6 are diagrammatic cross-sections of prior wafer bump fabrication process. As shown in FIG. 1, the prior UBM structure process is executed at the wafer stage, and a wafer 10 is provided firstly. As shown in FIG. 2, the wafer 10 includes the protecting layer 12 and electrode pad 14.
Next, as shown in FIG. 3, a coater is used to coat a polyimide layer 15 (PI layer) evenly on the wafer with spin coating, and then it is finalized into a film via soft bake on a hot plate. Then the UV exposure process is carried out, a photomask is used to cover the position of a predetermined via hole of the PI layer 15 without exposure to the light (the position of via hole are above the electrode pad 14). Later, the development process is executed, wherein the developing solution is used to remove the unexposed area by spray, and then titanium deposition is made by sputtering coating as an UBM structure 16.
Afterwards, a patterned photoresistance layer 18 (FIG. 4) is formed via photoresist coating process, exposure process and development process. Thereafter, a copper plate 20 (FIG. 5) with thick deposition is electroplated in the via hole of the patterned photoresistance layer 18. After that, the patterned photoresistance layer 18 is stripped first, and then the undesired UBM structure 16 is etched. Finally, the desired metal bump 22 (FIG. 6) is gained through photoresist coating, exposure, development, metal plating and resist strip process (not shown in the figure).
However, the UBM structure 16 and the metal bump 22 formed on the wafer 10 are processed with wafer size, its output is restricted by the wafer size, and the process is also complex, thus, its productivity is poor with slow output and high processing cost.
Therefore, it is an important subject to provide a method for fabricating UBM structure using electroless plating to develop a process to resolve various defects of the prior art above-mentioned, in order to promote the yield of products and reduce the fabrication cost.